You should google a guide on how to overclock your system. It varies between Intel and AMD. Also, if you have an OEM computer like a Dell, HP or the like, you cant** overclock due to having a stripped BIOS.

**The best way to overclock is to adjust BIOS settings, however, if your computer is OEM, you can not overclock, however, Ive heard you could use programs like SetFSB to overclock. Im not completely sure thats true, but thats what Ive heard.